Process for the production of polyolefine-based fibrids, and the fibrids obtained

Abstract

Polyolefine-based fibrids are produced by the abrupt expansion of a liquid mixture of molten polyolefine and solvent, this mixture being at high temperature and high pressure. The mixture contains the solvent, a polyolefine of normal molecular weight and a polyolefine of low molecular weight onto which a polar monomer has been grafted. The fibrids obtained possess a high proportion of grafted polyolefine on their surface.

I claim: 
     
       1. In a process for the production of polyolefine-based fibrids by the abrupt expansion of a liquid mixture of molten polyolefine and solvent, by passage through an orifice, the mixture being under pressure and temperature conditions which are such that the abrupt expansion causes the instantaneous vaporisation of the solvent and the solidification of the polyolefine in the form of fibrids, the improvement comprising subjecting to abrupt expansion a liquid mixture containing (1) a polyolefine of normal molecular weight, (2) said solvent and (3) a polyolefine of low molecular weight, onto which a polar monomer has been grafted. 
     
     
       2. Process according to claim 1, wherein the polyolefine of low molecular weight is an olefine polymer derived from ethylene and propylene. 
     
     
       3. Process according to claim 1 or 2, wherein the polyolefine of low molecular weight has a number-average molecular weight of less than 8,000. 
     
     
       4. Process according to claim 1 or 2, wherein the polyolefine of low molecular weight is a crystalline polyethylene wax or crystalline polypropylene wax. 
     
     
       5. Process according to claim 1 or 2, wherein said polar monomer comprises maleic anhydride. 
     
     
       6. Process according to claim 1 or 2, wherein the proportion of polar monomer in the grafted polyolefine of low molecular weight is between 0.1 and 5% by weight. 
     
     
       7. Process according to claim 1 or 2, wherein the amount of grafted polyolefine of low molecular weight in the liquid mixture is between 5 and 40% of the total weight of the polyolefines present in the mixture. 
     
     
       8. Process according to claim 1 or 2, wherein a polar monomer has not been grafted onto the polyolefine of normal molecular weight. 
     
     
       9. Process according to claim 1 or 2, wherein the grafted polyolefine of low molecular weight is manufactured by malaxating a mixture comprising the polyolefine of low molecular weight and the polar monomer at a temperature above the melting point of the polyolefine of low molecular weight. 
     
     
       10. Process according to claim 9, wherein the mixture which is malaxated additionally comprises a free-radical generator. 
     
     
       11. Process according to claim 10, wherein the polyolefine of normal molecular weight has a number-average molecular weight greater than 15,000 and the polyolefine of low molecular weight has a number-average molecular weight of less than 5,000. 
     
     
       12. Process according to claim 1 or 2, wherein the polyolefine of low molecular weight has a number-average molecular weight of less than 8,000 and the proportion of polar monomer in the grafted polyolefine of low molecular weight in between 0.1 and 5% by weight. 
     
     
       13. Process according to claim 12, wherein said polar monomer comprises maleic anhydride.